Today, a variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial PUFA production. Genetic engineering has demonstrated that the natural abilities of some hosts (even those natively limited to linoleic acid (LA; 18:2 ω-6) and α-linolenic acid (ALA; 18:3 ω-3) fatty acid production) can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs. Whether this is the result of natural abilities or recombinant technology, production of arachidonic acid (ARA; 20:4 ω-6), eicosapentaenoic acid (EPA; 20:5 ω-3) and docosahexaenoic acid (DHA; 22:6 ω-3) may all require expression of a Δ5 desaturase.
Most Δ5 desaturase enzymes identified thus far have the primary ability to convert dihomo-γ-linolenic acid (DGLA; 20:3 ω-6) to ARA, with secondary activity in converting eicosatetraenoic acid (ETA; 20:4 ω-3) to EPA (where DHA is subsequently synthesized from EPA following reaction with an additional C20/22 elongase and a Δ4 desaturase). The Δ5 desaturase has a role in both the Δ6 desaturase/Δ6 elongase pathway (which is predominantly found in algae, mosses, fungi, nematodes and humans and which is characterized by the production of γ-linolenic acid (GLA; 18:3 ω-6) and/or stearidonic acid (STA; 18:4 ω-3)) and the Δ9 elongase/Δ8 desaturase pathway (which operates in some organisms, such as euglenoid species and which is characterized by the production of eicosadienoic acid (EDA; 20:2 ω-6) and/or eicosatrienoic acid (ETrA; 20:3 ω-3)) (FIG. 1).
Based on the role Δ5 desaturase enzymes play in the synthesis of e.g., ARA, EPA and DHA, there has been considerable effort to identify and characterize these enzymes from various sources. As such, numerous Δ5 desaturases have been disclosed in both the open literature (e.g., GenBank Accession Nos. AF199596, AF226273, AF320509, AB072976, AF489588, AJ510244, AF419297, AF078796, AF067654 and AB022097) and the patent literature (e.g., U.S. Pat. No. 5,972,664 and U.S. Pat. No. 6,075,183). Also, commonly owned, co-pending applications having application Ser. No. 11/748,629 and Ser. No. 11/749,889 (filed May 17, 2007) disclose amino acid and nucleic acid sequences for a Δ5 desaturase enzyme from Euglena gracilis (see also Patent Publication US-2007-0277266-Δ1), while commonly owned, co-pending applications having application Ser. No. 11/748,637 and Ser. No. 11/749,859 (filed May 17, 2007) disclose amino acid and nucleic acid sequences for a Δ5 desaturase enzyme from Peridium sp. CCMP626 (see also Patent Publication US-2007-0271632-A1).
Although genes encoding Δ5 desaturases are known there is a need for additional varieties of these enzymes with varying enzymatic properties that are suitable for heterologous expression in a variety of host organisms for use in the production of ω-3/ω-6 fatty acids. Applicants have addressed the stated need by isolating genes encoding Δ5 desaturases from Euglena anabaena. 